Did your head feel any different while you were solving each problem? If so, that's because deep within the recesses of your cortex two different brain networks were battling with each other for control of your attention. Only one won.

In recent years, neuroscientists have identified two opposed brain networks: the default mode network (DMN) and the executive attention network (EAN). The standard view is that the DMN network is involved when we are engaged in internally focused tasks such as recalling deeply personal memories, daydreaming, sleeping, imagining the future, and trying to take the perspective of others. In contrast, the EAN network is thought to be involved when our attention is directed outward, and we must exert control over our limited attentional resources. For instance, the EAN is highly active when people are taking IQ tests (see here). When the DMN network is active the EAN network is quiet, and when the EAN network is active, the DMN network is quiet. But why?

In a recent study, Anthony Jack and colleagues argue that the crucial distinction between the two networks isn't internal vs. external attention but information processing. In particular, they argue that the DMN is associated with social information processing (reasoning about the minds of others), whereas the EAN network is associated with non-social information processing (reasoning about physical objects).

To test their hypothesis, they presented participants with social and physical scenarios (text and video), and asked them to predict the outcomes. The social scenes resembled soap operas, and were rich in emotional and moral content. In contrast, the mechanical scenarios described puzzles similar to the kind found in popular scientific puzzle books. While participants were thinking about the scenarios, their brains were being scanned by an fMRI machine.

What the researchers saw in the brain supported their theory. When people were reasoning about mechanical objects, the EAN brain network was activated and the DMN network was suppressed. In contrast, when people were engaged in social reasoning, the DMN network was active and the EAN network was supressed. These findings suggest we may have two fundamentally different versions of external reality that are constantly competing with each other for control of our perceived reality! After all, both tasks required external attention, were unfamiliar to the participants, and minimized the activation of personal memories.

It appears we may have two main modes of thought, one that focuses on social interactions and the mental states of others, and another mode of cognition that focuses on inanimate objects and the physical principles that make them work. Like the Necker cube, both modes of thought can't be engaged simultaneously.

The researchers suggest that the key is "cognitive context". Our primary mode of cognition in any moment in time has a powerful effect on the entire brain. When we must reason about the mental state of others, the brain recruits DMN resources and inhibits other brain networks. In contrast, when we must reason about physical objects, our social brain is shut down. This research is consistent with prior studies that have found that solving math problems suppresses empathy (giving charitable donations).

Our brain evolved the intelligent ability to switch brain networks depending on what kinds of mental representations are necessary for survival and reproduction. This is a good thing, since mixing mental representations can lead to the formulation of inappropriate strategies. As the researchers sensibly point out,

"It would be no less foolish to suppose that a person will continue in motion in a straight line unless acted upon by an external force, than it would be to suppose that a pool ball will alter its course because it wants to go into the pocket."

The mental representation of other people's minds and emotions is tightly linked to moral concerns (see here). Jack and colleagues argue that the inhibition between domains is driven by the need to differentiate members of our moral circle from objects suitable for manipulation. In terms of effective strategies, it would be a mistake to limit the actions one is willing to perform on an inanimate object out of a sense of compassion. They believe that antagonism between domains reflects a powerful human tendency to differentiate between conscious persons and inanimate objects in both our attitudes and modes of interaction.

There are widespread implications of these findings for our emerging understanding of different kinds of social minds, including autism and schizophrenia. For most people, our evolved brain networks automatically know when it's appropriate to come online and when it's best to lay dormant. For some people though, there isn't this automatic switching. For instance, those with autism have been shown to have an underactive DMN and an overactive EAN, which can lead to overthinking, a fascination with how objects work, and a lack of awareness of social subtly. In contrast, those with schizophrenia have been shown to have an overactive DMN and an underactive EAN, which can lead to overinferring people's intentions, disordered thought, and a breakdown of the boundary between self and other (see here for a review).

I think the jury is still out on how best to characterize the difference between the DMN and the EAN brain networks. The internal vs. external attention distinction may still be the correct one, especially considering how many people with altered brain networks report feeling literally trapped in their own heads. Nevertheless, I look forward to future research on this important topic, as it is sure to shed light what makes us human, as well as what makes us each unique.

Scott --
The results are certainly fascinating -- thanks for the article!

However there is one point that seems wrong to me:

"The results are also consistent with dual-process theories"

Only, it seems to me, if you are willing to throw out tne entire previous literature, experimental and theoretical, on dual-process theory. I don't see how this distinction at all lines up with the kinds of dual-process theories put forward by Kahneman, Evans, etc. The usual division in dual-process theory is, more or less, between cognition that requires deliberation, and cognition that is more "automatic"; and one can apply either of these modes of thought to either physical or social reasoning. It seems to me that here is yet another dichotomy in the theory of mind.

This also raises the question of what happens when you have to integrate social with physical reasoning e.g. to infer that if you talk to your wife from a room away, she may get annoyed because she will have trouble hearing you, or that if you see someone standing in front of a bus, you should push them out of the way. Is there reason to think that reasoning paths that combine both subject matters are more difficult?

Maybe it's just me, but I don't get the point of this article. If I see an object I don't need to concern myself with social issues because it is not alive, cannot be harmed, cannot harm me, etc. So why wouldn't those areas of the brain shut down? They're not needed.

If I see a person having a problem it's better for my brain to treat them as something like myself, alive, has feelings, can harm me, and so on. I can't treat them like an object.

So if the two areas are so different why is it any surprise that they aren't on at the same time? Your ears process sound, your eyes color and such. They both do only the job they were made for and are fine with or without the other. I can't see how they can really inhibit each other when they are unrelated. If I'm diligently looking for something I may miss hearing a sound, sure, but that's because I was focusing on what something looks like. I am deliberately filtering all else out. But it's not like you can't do two things at once. Or is that what they're trying to say? That you cannot deal with objects and people at the same time? But how? In what way? Like maybe I can't juggle and talk about personal problems at the same time or what?

At what point, in what situation are the brain's methods impractical or ineffective?

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I am ignorant of both neuroscience and psychology but upon reading your article, it occurs to me that the distinction between the two apparently exclusive modes of mental operation namely DMN and EAN may explain PTSD among war veterans : modern warfare is about executive planning , tactical and strategic decisions in a physical environment where physical manipulation and precision are key to success ....in fact a suppression of social empathy by objectifying the enemy may significantly increase the survivability of engaging soldiers. After all , firing rockets at precise angles , aiming at targets for neutralization are all accomplished with the expression of EAN.... But with repeated deployments as in the cases of our two most recent wars in the Middle East I wonder whether PTSD could be interpreted as a result of a cognitive conflict that a returning soldier faces : the over- reliance on EAN in the war-zone suddenly meets the demands for a previously suppressed DMN in the peace-zone .....that may explain the reason behind too many families of returning soldiers often complaining and describing their interaction as cold and superficial as if the returning soldiers are viewing their loved ones as objects ..